- RetroactiveMembershipService::createRetroactiveSubscription() now applies
  year-specific discounts from RuleEngine (SUBSCRIPTION_YEAR_ADJUSTMENT_{year})
  regardless of form input — server-side enforcement
- Retroactive wizard JS: uses year-specific rates (410/185 for 2023, 492/222
  for 2025+) and shows discount percentage visually per row
- total_amount = base - discount (dev fee excluded, added at invoice level)
- For paid rows: paid_amount includes dev fee since that's what was collected
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>